I'm replacing my kitchen sink. The existing sink is a double sink installed with two traps. Each sink has its own trap (1.5") and the pipes then meet in a wye. But when I was looking at a plumbing book I saw they had illustrated a double sink where the garbage disposal waste line (1.25" pipe) traveled horizontally to the other sink's waste line above the trap and then there was only one trap (1.5").

Which arrangement is better? Does it matter?